Strap stretching device



Oct. 24, 1944. N MARS 2,361,224

STRAP S THEICHING DEVICE Filed June-11, 1943 2 Sheets-Sheet 1 Z6 fail/24;

Y ATTORNE Oct. 24, 1944. N. MARS 2,361,224

STRAP STRETCHING DEVICE Filed June 11, 194s 2 sheets-sheet 2 P2 WITNEssEs: i A 4 INVENTOR` /VU/r Mars.

Y- v l BY l M f ATTORNEY Patented Oct. 24, 1944 UNITED STATES PATENT QFFICE Nick Mars, Sharon, Pa., assignor to= Westinghouse Electric & Manufacturing Cornpany, East-Pittsburgh, Pa., a corporation of Pennsylvania Application June 11', 1943, Serial No.- 4230*,4427

(Cl.l 25479) 9 Claims.

My invention relates to devices for stretching or tightening straps or bands of metal about a substantially solid mass and for maintaining a predetermined tension on the strap or band until it is fastened. The invention is adapted for applying steel bands about core structures of transformers where it is desirable to apply the band under a predetermined tension to maintain a constant predetermined pressure on the core parts enclosed by the band.

Devices for stretching or tightening a strap or band around a box or package are known but generallyr these articles are compressible and there is no particular reason for maintaining a'A predetermined tension of the strap thereon. When the article enclosed by the strap is compressible no rapid increase in the tension in the strap takes place upon operation of the stretcl'ifor controlling this tension, since a relatively slight stretching of the strap beyond the desired value will greatly increase the stresses on it, and may cause it to break, and failure to bring the strap to the desired tension will cause it to fail in its purpose of maintaining a predetermined desired force on the parts of the core.

In a copendi'ng application of John K. Hodnette Serial No. 377,472 led February 5, 1942", for Electrical induction apparatus, assigned to the same assignee as this invention, a core and coil assembly for transformers is disclosed in which the core 'parts are formed of loops of magnetic material wound layer upon layer and bonded together. The loops are then cut to form two U-shaped core portions which are assembled about the coils of the transformer and held in place by metal straps placed about the core loops. The strap is drawn to a predetermined tension and fastened in place to maintain a desired predetermined pressure upon the butt joints between the two U-shaped portions of the core loop. With the ordinary tool employed for stretching the strap about the usual type of article, it is difiicult to apply the desired pressure because a very slight increase in the stretch of the strap about the solid mass of iron greatly increases its tension. If this tension is much too greatthe strap will break; If it is not great enou'ghthe band will not maintain the desired pressure on the butt joints. In a copending application of John H. Bramble for Strap stretching devices, Serial No. 487,797 led May 20, 1943, assigned to the saine' assignee as this application, a: strapstre'tch-l ing device is disclosed provided with means for locking the operating mechanism when a predetermined tension onthe' strap has been effected. In this prior device in which the force is directly applied by the hand to a lever carried upon anothery lever which communicates the; force to the' operating mechanismen error may be introduced depending upon the force ofthe lever to' which the pressure is applied' as will be later explained.

lIt is anLv object of the present invention' to provide aA strap stretching device that will bring the strap' to the' desired' tension about a solid article and will not increase the tension above the desired amount.

It is more particularly an object of thel invention to provide a strapl stretching toolv of the character indicated in `which the point of the operating lever to which the pressure is applied by the hand of the operator does not vary the accuracy of the locking mechanism which limits the operation of the strap stretching device.

Other objects andadvantages of the invention will be apparent from the'following description of a preferred embodiment ofthe invention, reference being had to the accompanying drawings, in' which:

Figure l islanY elevational View of a core loop with the strap stretching device applied for stretching a steel' strap about the loop,

Fig. 2" is aside elevational View of the strap stretching device' with a part of the casing removed to'fillustrate the operating mechanism.

Fig. Bis a-sectional view ofa part of the device taken on the une' Iii- III 0f' Fig. 2.

Fig. 4 is a sld'e elevationalA view of the strap stretching device with a portion of the operating mechanism shown-insection;`

Fig. `5 is an exploded perspective view of a number of the partsy of the mechanismshcwn in disassembled relation.

Figs.` 6 and`7 are diagrams'illustrating the differencebetv'veen` theoperating principle of a prior art device and the device of this invention.

Referring tothe drawings and particularly to Fig. l thereof, the tool l is'shown in positionfor applying a` strap about a' core 1o`op2' comprising two U-shaped portions Bjarid l`V` having butt joints betweenV them along the adjoining surfaces 5. The'tool is used'to apply the metal strap 6 `about the core loop under apredeterminedtensionA so as to maintain a continuouspressure between the two U-sliaped portions 3 yand 4- at the butt joint surfaces 5; Asshown, one 1end 1' of the strap 6 extends over the cornerof the core and" along tightly against the foot or flange I1.

the surface of the loop passing under a fastening clip or sleeve 8 and bent at 9 to return through the clip or sleeve 8 which surrounds the strap, the strap continuing over the end portion 1 and passing about the core loop and again passing through the clip 8, the end II being positioned so as to be gripped by the tool for tightening it about the core loop.

After the strap has been pulled tight about the core loop by the tool I, the clip 8, which is in the form of a sleeve or band of metal about the two ends of the strap 6, is crimped or deformed sufficiently so that the edges of the clip and of the two ends of the strap passing through the clip are bent to vprevent the strap from loosening. This is done in a well known manner and is not a part of the invention and therefore is not described in greater detail.

The tool comprises a frame member I2 formed integrally with a handle I3, the frame member including a casing section I4 normally secured to the portion I2 by screws I5 to form a unitary part of the casing. A lower flat surface I6 of the complementary frame portions I2 and I4 extends horizontally in a plane substantially parallel with the handle I3. The lower portion of i the casing section I4 is provided with a foot or flange I1 projecting laterally therefrom and which extends horizontally above the surface of the article about which thesteel strap is to be stretched. The gripping member I8 mounted on the pivot pin I9 in the frame structure cooperates with the upper surface of the flange I1 for gripping the end II of the metal strap passing between the members I1 and I 8. The member I8 is provided witha serrated gripping lower surface 23 for tightly gripping the strap. The gripping member I8 is normally moved into engagement with the end II of the strap by means of a coil spring 24 which engages a recess 25 formed in the gripping member and bears against a flange 26 formed in the casing portion I4. It will be noted that the position of the gripping member I8 is such that as the end II of the strap 6 is pulled toward the right as viewed in Fig. 1, it tends to tighten the grip of the member I8 on the strap and to press it more The casing members I2 and I4'are provided with a horizontal guideway which is adapted to receive and guide the movement of a rack bar 28 formed with an enlarged head 29 at one end thereof and provided with teeth 3| on the upper side thereof. The head 29 may be provided with gripping members similar to the members I1 and I8 but is shown as provided with a foot or flange member 32 which is positioned below the end II of the metal strap and above theother end of the strap to the right of the clip 8 as shown in Fig. 1. An upper member 33 is positioned above the end Il of the strap and mounted on a pin 34 attached to the head 29. The members 32 and 33 provide the jaws of the duckbill for engaging the end of the clip 8 for forcing the clip in a direction away from the gripping members I1 and I8 mounted on the frame.

The gripping members comprising the parts I1 and I8 and the gripping member comprising the parts 32 and 33 form two relatively movablev gripping members which are operated away from each other for the. purpose of stretching the strap 6 about the core loop. The mechanism for effecting this operation comprises a pinion having teeth for engaging the teeth 3| on the rack bar. This'pinion is not shown in the drawings but is integrally attached to the shaft 31 shown in Fig. 2 extending between the two walls of the casing sections I2 and I4 and upon which the ratchet wheel 38 is also fixedly mounted, so that the pinion (not shown) and the ratchet wheel 38 rotate together. The ratchet wheel 38 is provided with teeth 39 adapted to be engaged by a pawl 42 which is located within the chamber between the casing members I2 and I4 and pivotally connected by a pin 45 to an extension of an operating lever 46 which is pivotally mounted on a pin 41 carried by the casing members. The upward movement of the lever 46 from the position illustrated in Figs. 1, 2 and 3 causes the pawl 42 to move downwardly in engagement with the teeth 39 of the ratchet wheel tolmove the ratchet wheel 38 and the pinion engaging the teeth 3I i-n a clockwise direction to move the head 29 of the rack bar toward the left as shown in the drawings.

The pawl 42 is normally held in engagement with the teeth 39 of the ratchet wheel by a spring 48 mounted about a pin 49, the lower end of which is positioned in av socket 5I formed in the upper side of a detent 52 which is pivotally mounted on a pin 53 mounted in the casing structure. The detent is provided with a tooth 54 adapted to engage the teeth 39 of the ratchet Wheel to prevent reverse rotation thereof. The upper end of the pin 49 extends through a bore in alprojecting head 56 forming a part of the pawl 42. The lower end of the spring 48 engages a collar 51 on the pin 49 and the upper end of the spring 48 engages the projecting head 56. When the pawl is operated to rotate the ratchet wheel 38 the detent 52 rides over the teeth 39 of the ratchet wheel and engages a tooth in a new position to hold the ratchet wheel against reversed rotation during a reverse movement of the pawl 42.

To permit therelease of th'e ratchet wheel and to allow a reverse movement of the ratchet wheel 38 and pinion and a return movement of the head 29 toward the frame, after these parts have been actuated to effect the desired stretching of the steel strap 6 the detent 52 is moved upwardly about its pivot 53 and the pawl 42 is simultaneously moved out of engagement with the ratchet teeth 39. This operation is effected by a releasing member 60 mounted on a shaft 6| and provided with a projection 62 adapted for engaging the under side of the detent 52 and provided also with an upwardly extending part 63 which serves as a cam to effect movement of the pawl 42 away from engagement with the teeth 39 of the ratchet wheel. Any suitable means may be provided for rotating the shaft 6| in a clockwise direction to effect the releasevof the pawl 42 and the detent 52 to engage the teeth of the ratchet wheel 38.

In order to provide for limiting the pressure or tension to be applied to the steel strap 6, a second 'lever 10 is provided having one end mounted on the pivot 41 upon which the lever 46 is mounted. The lever 10 is a channel-shaped member having two outer side portions 1I connected by a web portion 12, the web portion being positioned below the lever 46 and the side portions being adapted to move along opposite sides of the lever 46. The levers 46 a'nd l0 are mounted directly below the handle I3 so that the lever 18 and the handle I3 together provide a hand grip whereby the two levers 10 and 46 may be moved upwardly by the fingers of the hand engaging the lever 10. A rack 14 is provided extending downwardly from the handle I3 and provided with teeth 15 on the inner side thereof po'- sitioned adjacent'the pathof movement of thel and engaging: the web portion 12 of the lever T0..

A locking member 8| isv shown having a cylindrical shaft portion 82 extending through a borev 33 in thebody of the lever 46 for slidable endwise` movement therein. The member 8| is provided4 with a tooth 84` that is adapted to engage between the teeth 7.5; on` the rack, member 14, and is providedtalso withf an outer memberl 85 extending on the outer side ofv the rack 14 for providing readyV manual operation of the locking member to release` ther tooth 84f from engagement with the racl; A spring 86` is provided about the inner encl` portion of the shaft 82 between an abutment portion` 8"?y of the lever: 46` and-an abutment member. 88v attached by apivot pin 89 to the shaft 82 and provided witha socket or cup for receiving one end oi the spring 86. A latch member 9| is shown mountedV on aA pin 92 extending between the opposite sides of a recess 93 in the upper side of the lever it and having an outer end portion 98 that is adapted to engage the abutment member 88 carried on the shaft 82 for retaining the lock member in its releasedl position with the spring 86 compressed. A spring 94v is provided positioned between a` cupsleeve 95v and a plug 96 in a bore 8l through the lever 48 for engaging the righthand end. oi the'latch 9| to maintain the end 98 lowered against the` abutment 88. A pin ||J| is shown extending upwardly through a bore |02 in the lever 46; the lower end being adapted to engage the 'web portion '|24 of the lever 10 and the upper end portion being adapted to engage a setscrew |83 mounted inthe latch 9|. Slots Ill and |85 are provided in the shaft portion 82 of the locking member through which the pins Il and the spring and sleeve construction 94 and 95 extend respectively in order to permit free endwise movement of the shaft 82 within the required limitsof movement. In Fig. 4 thelocking member is shown inan intermediate position midway between the position in which the latch 9a will be positioned about the abutment B3 'and the position in which the tooth 84 will be positioned between teeth 'I5 inthe rack' 14;

After thesteel strap has been positioned about the core loop as shown in Fig. 1, with the end extending through the clip 8 and bent at 9 under the main body of the stra-p. Gand the other end of the strap extending through the clip 8 between the. jawsv 32 and 33 of. the tool, and gripped between the members |8- and the tool is ready for operation to stretch the strap 6 aboutV the core loop 2. The locking member 8| is forcedI toward the left and the end` 93 of. the latch 9|, that is biased 'by the spring 94, is positioned against the abutment 88 to retain it in its latched position to permit free movement of the lever 46 about its pivot pin 41, The hand is then grasped about away' from the frame portion of the tool. The end I of the' steel strap slides betweenl the members 32l and. 33' which members force the clip B toward the left, the end of the strap being held by the members and H8 as the strap is tightened about the co-re. The force applied to the lever is conveyed to the lever 48 through the springs Tl. As the strap tightens about the core, the force necessary for successive movements of the pawl increases so that as the force: conveyed from the lever: i8 to the lever 4G correspondingly increases, the lever 'lll comes closer to the lever it and upon the transmission of ay predetermined force between the two levers the pin |0| is moved upwardly'by the web member 'l2 of the lower lever against the end of the setscrew |03, so as to move the end 83y of the latch member upwardlyabove the edge of the abutment member 98 as shown in Fig; 4, thus releasing the locking member to permit the spring 86 to force it toward the right until the tooth 81|y engages between the teeth 'E5 of the rack 1d to lock the lever system against further movement of the pawl and further tightening of the strap. The particular force required to trip the latch 9| may be adjusted by the adjusting screw |03 `and by the number and the character of the springs 'l1 positioned between the two levers t5` and 18.

Fig. 6 is a diagrammatic View of a lever system of a prior stretching tool in which the levers similar to applicants levers l5 and 18 are employed except that the lower lever 18 is pivoted to the upper lever 45 at the outer end P of the two levers, the left end as shown at O being the pivot point corresponding to the pin 47|. The force R is the force applied to the pawl which it is desired to bel of a predetermined value whenv the latching member trips. In the device shown in Fig. 6, a single spring Sl is shown between the-V two levers ll and 'i8 and a pin corresponding to applicants pin |0| is provided for tripping the latch to permit the locking member to be moved to engage the teeth l5. and prevent further operation of the device after a predetermined force is applied between the two levers i6 and 10. If theY force is applied directly at the point Pl so that.

the entire force is transmitted from the lever 10 to the lever 46 through the spring SI, the toolworks as intended. If, however, the center of the force is applied nearer to the outer end of the lever P2 or nearer the point of connection P between the two levers, a portion only of the` total applied force will be transmitted to the lever 4E through the spring Si. For example, if.

the force is applied `at F, a portion of this force.

will be communicated between the point PI and the spring Sl to the lever 46 and, a portion of it` through the point P so that the force applied. to the pawl indicated by R is not accurately measured by the tension on the spring Sl.

This error is overcome inl the arrangement of the levers provided in applicants tool as shown in Fig. 'l` The two levers 46 and 'I8 are pivoted about the same fixed pivot at O and all of the force between the two levers is conveyed through the several springs 'Vi so that the relative positions of these two levers, as measured by the compression of the springs TI, is a true measure ticular portion of the handle and lever to which the force is applied by the hand of the operator.

It will be understood by those skilled in the art that modiiications may be made in the details of the structure illustrated and described without departing from the spirit of my invention, and it is intended that the above description of a preferred embodiment of the invention be taken as illustrative of the invention and not in a limiting sense.

I claim as my invention:

1. The combination in a strap stretching device, of a pair of relatively movable members, means carried by each of said relatively-movable members and constructed to grip the ends of a flat metal strap with said ends overlapping one above the other, and means for moving said relatively-movable members away from each other for drawing said strap taut around an article and maintaining said overlapping portions in taut condition including a lever pivotally mounted at its inner end on the frame of said device, a second lever also pivotally mounted on the frame adjacent the inner end of the rst-named lever and extending outwardly along the first-named lever, a plurality of compressible members positioned between said two levers and spaced at intervals along the lengths thereof for transferring force applied to the second-named lever to the first-named lever for operating the stretching device, and means operable upon the application of a predetermined force between said levers for locking said rst-named lever against further movement.

2. The combination in a strip stretching device of a frame, a rack bar having movement in said frame, means carried by said bar and said frame for engaging a strap, means carried by said frame including a ratchet wheel for effecting movement of said rack bar relative to said frame, a pawl adapted to engage said ratchet wheel, a handle mounted in fixed position on said frame, a lever pivotally mounted at its inner end on the frame of said device for operating said pawl, a second lever pivotally mounted adjacent the inner end of the first-named lever and extending outwardly along the rst-named lever and adapted to be manually engaged and operated, a plurality of spring members positioned between said two levers and spaced at intervals along the lengths thereof for transferring force from the manually engaged second-named lever to the first-named lever for operating the stretching device, and means operable upon the application of a predetermined force between said levers for locking said first-named lever against further movement.

3. The combination in a strap stretching device, a pair of relatively movable members, means carried by each of said relatively movable members and constructed to grip the ends of a flat metal strap with said ends overlapping one above the other, and means for moving said relatively movable members away from each other for drawing said strap taut around an article and maintaining said overlapping portions in taut condition and comprising a lever pivotally mounted at its inner end on the frame of said device, a second lever pivotally mounted adjacent the inner end of the first-named lever and extending outwardly along the first-named lever and adapted to be manually engaged and operated, the second lever being channel shaped having side portions spaced to move along opposite sides of the rst-named lever and a web portion connecting the side portions, a plurality of recesses along the rst-named lever adjacent the second-named lever, and spring members therein adapted to engage the web portion of the secondnamed lever for biasing the two levers away from each other and for communicating force applied to the manually operated second-named lever to the iirst-named lever for operating the relatively movable member, and means operable upon the application of a predetermined force between said levers for locking said first-named lever against further movement.

4. The combination in a strap stretching device of a frame, a rack bar having movement in said frame, means carried by said bar and said frame for engaging a strap, means carried by said frame including a ratchet wheel for effect- `ing movement of said rack bar relative to said frame, a pawl adapted to engage said ratchet wheel, a handle mounted in xed position on said frame, a lever pivotally mounted at its inner end adjacent the frame of said device for operating said pawl, a second lever pivotally mounted on the innerend of the first-named lever and extending outwardly along the first-named lever, the second lever being channel shaped having side portions spaced to move along opposite sides of the rst-named lever and a web portion connecting the side portions, a plurality of recesses along the first-named lever adjacent the secondnamed lever, and spring members therein adapted to engage the web portion of the second-named lever for biasing the two levers away from each other and for communicating force applied to the second lever to the first-named lever for operating the pawl, and means operable upon the application of a predetermined force between said levers for locking said first-named lever against further movement.

5. The combination in a strap stretching device, a pair of relatively movable members, means carried by each of said relatively movable members and constructed to grip the ends of a flat metal strap with said ends overlapping one above the other, and means for moving said relatively movable members away from each other for drawing said strap taut around an article and maintaining said overlapping portions in taut condition comprising a lever pivotally mounted at its inner end on the frame of said device, a second lever pivotally mounted adjacent the inner end of the first-named lever and extending outwardly along the iirst-named lever for operating the first-named lever, the second lever being channel shaped having side portions spaced to move along opposite sides of the first-named lever and a web portion connecting the side portions, a plurality of recesses along the first-named lever adjacent the second-named lever, and spring members therein adapted to engage the web portion of the second-named lever for biasing the two levers away from each other and for communicating force applied to the secondnamed lever to the iirst-named lever, and means operable upon the application of a predetermined force between said levers for locking said rstnamed lever against lfurther movement, said means including a locking member slidably mounted on said rst-named lever and biased for movement outwardly from the pivotal support of the lever, a rack extending along the path of travel of the outer end of the lever and provided with teeth for receiving the locking member, a latch member normally retaining the locking member from engagement with said rack,

and means for tripping the latch member upon a predetermined relative movement of said two levers upon compression of the biasing means between them.

6. The combination in a strap stretching device of a frame, a rack bar having movement in said frame, means carried by said bar and said frame for engaging a strap, means carried by said frame including a ratchet wheel for effecting movement of said rack bar relative to said frame, a pawl adapted to engage said ratchet wheel, a handle mounted in xed position on said frame, a lever pivotally mounted at its inner end adjacent the frame of said device for operating said pawl, a second lever pivotally mounted on the inner end. of the iirst-named lever and extending outwardly along the rst-named lever, the second lever being channel shaped having side portions spaced to move along opposite sides of the rstnamed lever and a web portion connecting the side portions, a plurality of recesses along the first-named lever adjacent the second-named lever, and spring members therein adapted to engage the web portion of the second-named lever for biasing the two levers away from each other and for communicating force from the second-named lever to the first-named lever for operating the pawl, and means operable upon thc application of a predetermined force between said levers for locking said rst-named lever against further movement, said means including a locking member slidably mounted on said rst-named lever and biased for movement outwardly from the pivotal support of the lever, a rack extending along the path of travel of the outer end of the lever and provided with teeth for receiving the locking member, a latch member normally retaining the locking member from engagement, with said rack, and means for tripping the latch member upon a predetermined relative movement of said two levers upon compression of the biasing means between them.

'7. The combination in a strap stretching device, of a pair of relatively movable members, means carried by each of said relatively movable members and constructed to grip the ends of a at metal strap with said ends overlapping one above the other, and means for moving said relatively movable members away from each other for drawing said strap taut around an article and maintaining saidA overlapping portions in taut condition including a lever pivotally mounted at its inner end on the frame of said device, a manually operable second lever for operating the first-named lever also pivotally mounted on the frame adjacent the inner end of the rst-named lever and extending outwardly along the firstnamed lever, compressible means positioned be tween said two levers for transferring force applied to the second-named lever to the irstnamed lever for operating the stretching device, and a single locking means operable upon the application of a predetermined force between said levers for locking said iirst-named lever against further movement in either direction.

8. The combination in a strap stretching device of a frame, a rack bar having movement in said frame, means carried by said bar and said frame for engaging a strap, means carried by said frame including a ratchet wheel for effecting movement of said rack bar relative to said frame, a pawl adapted to engage .said ratchet wheel, a handle mounted in fixed position on said frame, a lever pivotally mounted at its inner end on the frame of said device for operating said pawl, a second lever pivotally mounted adjacent the inner end of the first-named lever and extending outwardly along the first-named lever, a spring member positioned for transferring force from the second-named lever to the first-named for operating the stretching device, and a single locking means operable upon the application of a predetermined force between said levers for locking said first-named lever against further movement in either direction.

9. The combination in a strap stretching device, a pair of relatively movable members, means carried by each of said relatively movable members and constructed to grip the ends of a iiat metal strapwith said ends overlapping one above the other, and means for moving said relatively movable members away from each other for drawing said strap taut around an article and maintaining said overlapping portions in taut condition, a lever pivotally mounted at its inner end on the frame of said device, a second lever pivotally mounted adjacent the inner end of the first-named lever and extending outwardly along the first-named lever, the second lever being channel shaped and having side portions spaced to move along opposite sides of the first-named lever and a web portion connecting the side portions, biasing means adapted to engage the web Iportion of the second-named lever for biasing 

